correctly fails to compile, since both import statements declare an identifier named types. However, the file/line info displayed with the error message from the compiler currently says the error occurred on line 1 of b/types.nim, which may be misleading - the actual error is in completely different file to where the compiler says the error is.
Locate 'attempt to redefine' errors at the import statement rather th…
…an at the first line of the imported module. Fixes #4541.